[RPG] How to allow player agency in situations with predetermined outcomes

I would do this with roleplaying and whatever social combat rules your system uses. The level of detail is determined by how important you want the trial to be in your game. If you are not using a system with social combat, you can also model it with "chase" or "extended contest" rules, anything where success accrues over time can probably be kit-bashed into doing the trick.

My problem with Jenga is that you're not building something stronger as you progress, you're making something weaker. It just completely goes against the thing you're modeling.

Here's how I would handle it:

• Determine the skill of the lawyers involved. Or the skill of the PC and NPC who will be the primary speakers at the trial.
• Determine the number of successes required to constitute victory.
• Ask what the players want to do in terms of preparation. Typical activities might include:
  • Gathering additional evidence
  • Tracking down witnesses
  • Bribing, intimidating, murdering, and otherwise influencing judges and / or jurors
  • Studying the law
  • Finding precedents
  • Tracking down the real criminal
  • Getting someone else to confess
  • Convincing frightened people to testify

Each of those activities could be an encounter or string of encounters. In the run-up to the trial, decide what the PCs get for succeeding or failing in these efforts. Smaller benefits could be modeled as skill bonuses, while larger benefits could be "free" successes to apply.

So if most of the PCs go out to convince people who can confirm the accused's alibi to testify, you can play that out. When they succeed give them a bonus to one or more "lawyer" skill rolls for use during the trial. Meanwhile, the (presumably imprisoned) accused PC is trying to track down the real killer in his prison. If he can get the guy to confess, you can grant them some number of free successes, based on how credible the confession is, etc..

In this way, you keep everyone engaged in the pre-trial process, and everyone gets to see their contributions contribute concretely during the trial.

I ran into this too, with the diverse characters and the hard first-session railroad. I became disillusioned because they wanted me to tell a story and I wanted a sandbox, but the result was the same: I had no desire left to run it.

It's awful advice, but my conclusion was that not every game is made to be continued, and it's only a failure if it's pushed beyond the number of sessions it can happily support.

You might be able to completely turn it around, but it's a tall order to change the game into something more like what you'd be happy with when it's contrary to what the players are already enjoying about the game. If you can pull it off, do it. You might consider offering to give up the GMing of this game to another player, and become a player yourself.

But if you can't pull it off, letting the game die peacefully is kinder to you and the other players. The sooner a doomed game is done, the sooner you can start on the next awesome one!